REDOX-INDUCED P-O AND MN-MN BOND CLEAVAGES AT DIMANGANESE CARBONYL CENTERS - SYNTHESIS AND OXIDATION REACTIONS OF THE DIANION [MN2(MU-P(OET)2)(MU,ETA-2-OP(OET)2)(CO)6]2-

Chemical reduction of the unsaturated dihydride [Mn2(mu-H)2(CO)6{mu-(EtO)2POP(OEt)2}] with several reagents (Na-Hg, K, etc.) promotes dihydrogen elimination and an intramolecular P-O bond oxidative addition of the diphosphite ligand, yielding [Mn2{mu-P(OEt)2}{mu,eta2-OP(OEt)2}(CO)6]2-(2). Chemical oxidation of 2 with 2 equiv of [FeCP2]PF6 in tetrahydrofuran at -80-degrees-C results in metal-metal bond cleavage and formation of thermally unstable species, possibly incorporating two tetrahydrofuran molecules. Thermal decomposition of the latter at room temperature yields [Mn2(mu-P(OEt)2}{mu,eta2-OP(OEt)2}(CO)8] or, if a phosphine L is present, [Mn2{mu-P(OEt)2}{mu,eta2-OP(OEt)2}(CO)7(L)]. If a diphosphine L2 is used during oxidation (L2 PCH2PMe2, Ph2PCH2PPh2), two isomers formulated as [Mn2{mu-P(OEt)2}{mu,eta2-OP(OEt)2}(CO)6-(L2)] and [Mn2{mu-P(OEt)2}{mu,eta2-OP(OEt)2}(CO)6(mu-L2)] are obtained, but only the latter is isolated when L2 = (EtO)2POP(OEt)2. A possible reaction pathway for the above reactions is proposed on the basis of the compounds isolated and of the detected intermediates. The structures of the new complexes are discussed on the basis of IR and NMR data as well as of the X-ray crystal structures of [Mn2{mu-P(OEt)2}{mu,eta2-OP(OEt)2}(CO)7(PPh3)] (4a) and [Mn2{mu-P(OEt)2}{mu,eta2-OP(OEt)2}(CO)6(Me2PCH2PMe2)] (6a). Crystals of 4a are triclinic, space group P1BAR with Z 2 in a unit cell of dimensions alpha = 21.127(8) angstrom, b = 10.503(5) angstrom, c = 10.099(6) angstrom, alpha = 65.01(2)-degrees, beta = 73.45(2)-degrees, and gamma = 76.05(2)-degrees. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares on the basis of 3711 observed reflections to R and R, values of 0.0425 and 0.0560, respectively. In the molecule the two manganese atoms, displaying an octahedral coordination, are bridged through the P atom by the ethoxyphosphido group and through the P and 0 atoms by the phosphonate group. The coordinations around the manganese atoms are completed by seven terminal carbonyl ligands and a triphenylphosphine ligand, which is trans to the phosphido group and cis to the oxygen-donor atom of the phosphonate ligand. Crystals of 6a are monoclinic, space group P2(1)/c with Z = 4 in a unit cell of dimensions a = 14.451(5) angstrom, b = 10.469(3) angstrom, c = 20.087(7) angstrom, and beta = 91.36(2)-degrees. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least squares on the basis of 1625 observed reflections to R and R(w) values of 0.0408 and 0.0542, respectively. The structure of Ga is very similar to that of 4a, except that now a diphosphine ligand chelates the manganese atom bearing the 0-donor atom of the phosphonate ligand with two P atoms trans to the phosphido and carbonyl ligands, respectively.